1. Field of the Invention
The present invention relates to a lens activating device, and in particular, to a lens activating device for driving lens of a micro imaging module.
2. Description of Related Art
Recently, it becomes more and more popular for portable devices such as mobile phones or PDA to be equipped with an imaging module. Furthermore, since the market requires these portable devices to have more powerful functions and smaller sizes, it is necessary for the imaging module to generate high quality pictures and to be of small size accordingly. One improvement of picture quality is to increase the number of pixel. The pixel number of an imaging module has already increased from the VGA-level 30 pixels to 2, 3 or even 8 million pixels, which is now common in the market. Another improvement lies in the definition of the image. Thus, the imaging module of a portable device also develops from a fixed-focus mode to auto-focus mode or even optical zoom mode.
The auto-focus mode employs the principle of moving the lens in the imaging module suitably according to various distances of targets, whereby the optical image of the desired target can be focused correctly on an image sensor so as to generate a clear image. The common ways of activating the lens to move in the imaging module include activating by a step motor, piezoelectric motor and voice coil motor (VCM)
In general, the voice coil motor is constituted by disposing a coil in the magnetic circuit of permanent magnets. According to Fleming's left hand rule, when an electric current passes through the coil, a pushing force may be induced by the permanent magnets, thereby moving a supporting base connected to the permanent magnets and thus driving the lens assembly fixed in the supporting base. With the adjustment of current passing through the coil, the optical zoom mode and the auto-focus mode can be achieved.
Please refer to FIG. 1. JP 2006-201525 discloses an elastic piece 1a of a lens driving device, which includes an outer ring 11a, three supporting arms 12a extending and bending continuously from the inner wall of the outer ring 11a, and an inner ring 13a provided in the outer ring 11a and connected to the distal end of the supporting arm 12a. With the inner ring 13a of the elastic piece 1a being fixed to the lens assembly of the lens driving device and the outer ring 11a being fixed to the supporting base, the elastic force of the elastic piece 1a can allow the voice coil motor to be positioned and restored.
Please refer to FIG. 2. JP 2003-295033 discloses an elastic piece 1b of a lens driving device, which includes two curved arms 11b that are symmetric with each other and are formed into C shape and a connecting piece 12b. After the elastic piece 1b is pressed, the curved arm 11b is bent at a first positioning end 111b and then bent reversely to form an elastic arm 112b. The distal end of the elastic piece is formed with a second positioning end 113b. The connecting piece 12b is connected with the two curved arms 11b for positioning these two elastic arms. In mounting, the first positioning end 111b and the second positioning end 113b of the two curved arms 11b are positioned on the lens assembly and the supporting base respectively. After cutting off the connecting piece 12b, the two curved arms 11b can allow the voice coil motor to be positioned and restored.
However, in the above two patent documents, the elastic piece is driven by the lens assembly to move vertically (axially). Thus, the lens assembly may rotate slightly to hit the elastic piece. As a result, the elastic piece may suffer damage and even get failure.
Furthermore, the elastic piece is formed by a pressing process. If the construction of the elastic piece is more complicated, such as that in JP 2006-201525, in which the supporting arm is formed with continuous bends, it is more difficult to develop the press-forming molds for the supporting arm. As a result, the production cost may be inevitably increased and the yield of products may be deteriorated.
According to the JP 2003-295033, after feeding and press-forming the elastic piece, a further cutting process is needed (i.e. cutting off the connecting piece). Thus, the production cost and working hours are increased undesirably.
Please refer to FIGS. 3 and 4 again. JP 2008-026619 also discloses a lens driving device, in which an upper elastic piece 91a is sandwiched between an outer casing 93a and a top frame 94a. An outer ring 912a of the upper elastic piece 91a is fixed between a casing 93a and the top frame 94a. The inner ring 912a of the upper elastic piece 91a is fixed to a lens base 96a, thereby positioning and restoring the lens base 96a. A lower elastic piece 92a is sandwiched between a bottom frame 95a and the lens base 96a. With an insulating ring 97a being disposed around the lens base 96a to press the outer ring 921a of the lower elastic piece 92a, the lower elastic piece 92a can be fixed to the bottom frame 95a. In this way, the outer ring 921a and the inner ring 922a of the lower elastic piece 92a can be secured without flexing.
In addition, it is more important to appreciate that a wrist 913a of the upper elastic piece 91a is connected to the inner ring 911a and the outer ring 912a, and it is used as a flexible section when the outer ring 911a moves with respect to the inner ring 912a. However, such a wrist 913a is formed with continuous bends, so that it cannot be manufactured easily and may suffer damage.
Therefore, in view of the above-mentioned drawbacks, the present Inventor proposes a reasonable and novel structure based on his expert experience and delicate researches so as to solve the drawbacks in prior art.